1. Field of the Invention
The present invention relates generally to sleeve valve systems for aspirating internal combustion engines, and to internal combustion engines with tubular sliding valves for enhanced aspiration. More particularly, the present invention relates to reciprocating sleeve valve systems for engines equipped therewith of the general type classified in United States Patent Class 123, Subclasses 84, 188.4, and 188.5.
2. Description of the Related Art
A variety of aspiration schemes are recognized in the internal combustion motor arts. In a typical four-cycle firing sequence, gases are first inputted and then withdrawn from the combustion chamber of each cylinder interior during reciprocating piston movements caused by the crankshaft. Gas pathways must be opened and closed during a typical cycle. During the intake stroke, for example, an air/fuel mixture is suctioned through an open intake passageway into the combustion chamber as the piston is drawn downwardly within the cylinder. The intake passageway is typically opened and closed by some form of reciprocating valve mechanism that is ultimately driven by mechanical interconnection to the crankshaft. The combustion chamber must be sealed during the following compression and power strokes, and the valve mechanisms must be closed to block the ports. During the following exhaust stroke, exhaust ports must be opened to discharge spent gases from the combustion chamber.
Spring-biased poppet valves are the most common form of internal combustion engine valve. Typically, poppet valves associated with the intake and exhaust passageways are seated within the cylinder head above the combustion chamber proximate the cylinder and piston. Typical reciprocating poppet valves are spring biased, assuming a normally closed position when not deflected. In a typical arrangement, the bias spring coaxially surrounds the valve stem to maintain the integral valve within the matingly-configured valve seat. Poppet valves are typically opened by mechanical deflection from valve train apparatus driven by camshafts. Typical overhead-valve motor designs include rocker arms comprising reciprocating levers driven by push rods in contact with camshaft lobes. When the camshaft lobe deflects a pushrod to raise one end of the rocker arm, the opposite arm end pivots downwardly and opens the valve. When the camshaft rotates further, the rocker arm relaxes and spring pressure closes the valve. With overhead-cam designs camshafts are disposed over the valves above the head, and valve deflection is accomplished without push rods or rocker arms. Overhead camshafts push directly on the valve stem through cam followers or tappets. Some V-configured engines use twin overhead camshafts, one for each head. Some enhanced DOHC designs use two camshafts in each head, one for the intake valves and one for the exhaust valves. The camshafts are driven by the crankshaft through gears, chains, or belts.
Despite the overwhelming commercial success of poppet-valve designs, there are numerous deficiencies and disadvantages associated with poppet valves. Although poppet valve designs provide manufacturing advantages and cost savings, substantial spring pressure must be repeatedly overcome to properly open the valves. Spring pressure results in considerable drag and friction which increases fuel consumption and limits engine RPM. Poppet valve heads are left within the fluid flow passageway, despite camshaft deflection, and the resulting obstruction in the gas flow pathway promotes inefficiency. For example, back pressure is increased by the valve mass obstructing fluid flow, which contributes to turbulence. Poppet valves are exposed to high combustion chamber temperatures, particularly during the exhaust stroke, that can promote deformation and wear. Thermal expansion of exhaust valves, for example, can interfere with proper valve seating and subsequent sealing, which can decrease combustion performance.
Many of these disadvantages are amplified in high-horsepower or “high R.P.M.” applications. Valve deflection in high power applications is often extreme, increasing the amplitude of valve deflection or travel. Damaging valve-to-piston contact can result. As a means of attenuating the latter factor, some pistons are designed with valve clearance regions, but these piston surface irregularities can deleteriously affect the combustion charge and fluid flow through the combustion chamber. Another problem is that the applied drive forces experienced by the valves are asymmetric. The extreme forcing pressure applied by the camshaft to open the valves, for example, is not as uniform as the spring closing pressure. Disharmony between the opening and closing forces contributes to valve lash and concomitant timing problems that interfere with power generation and limit engine R.P.M. Of course, in high power systems involving four or more valves per cylinder, the problems and disadvantages with poppet valve engines are increased proportionally.
So-called “rotary valves” have been proposed for replacing reciprocal poppet valves. Typical rotary valve designs include an elongated tube or cylinder machined with a plurality of gas flow passageways that admit or pass gases. The rotary valves are not reciprocated; they are rotated about their axis to expose passages defined in them in directions normal to their longitudinal axis. Rotary valves must be timed properly to dynamically align their internal passageways with the fluid flow paths of the engine during operation. When rotated to a closing position, the rotary valve passageways are radially displaced, obstructing the normal flow pathways and sealing the engine for firing or compression strokes.
One advantage espoused by rotary valve proponents is the relative simplicity of the design. Further, rotary valves do not penetrate or extend into the cylinder, avoiding potential mechanical contact with the piston, and minimizing fluid flow obstructions. However, the biggest problem with rotary valves relates to ineffective sealing. Although much activity and research has been directed to rotary valve sealing designs, commercially feasible systems have not been perfected. Rotary systems provide inefficient cylinder sealing, lessening firing efficiency, and reducing compression pressure because of leakage. Further, rapid wear of such systems increases the aforementioned problems.
Sliding valves of many configurations are also known in the art. Typical slide valves may be hollow and tubular, or planar, or cylindrical. They are reciprocated within a tubular valve seat region proximate the combustion chamber to alternately open and then close the intake and exhaust passageways. Like rotary valves, sliding valve designs have hitherto been difficult to seal effectively, with predictable negative results.
U.S. Pat. No. 2,080,126 issued May 11, 1937 to Gibson shows a sliding valve arrangement involving a tubular valve driven by a secondary crankshaft. Its reciprocating axis is parallel to the axis of piston deflection. Ports arranged at the side of the piston are alternately opened and closed by piston movements, and gases are conducted through and around portions of the piston exterior.
A similar arrangement is seen in U.S. Pat. No. 1,995,307 issued Mar. 26, 1935, and U.S. Pat. No. 2,201,292, issued May 21, 1940, both to Hickey. The latter patents show designs that aspirate a single working cylinder with a pair of tubular, reciprocating valves that are mounted on either side of the piston and driven by secondary crankshafts. The aspirating valves are forcibly reciprocated between port blocking and port aligning positions. The valves are aligned at an angle slightly off of parallel with the axis of the cylinder.
Other examples of engines with tubular, reciprocating slide valves that move in a direction generally parallel with the drive piston axis are provided by U.S. Pat. Nos. 1,069,794; 1,142,949; 1,777,792; 1,794,256; 1,855,634; 1,856,348; 1,890,976; 1,905,140; 1,942,648; 2,160,000; and 2,164,522 that are largely cumulative.
Hickey U.S. Pat. No. 2,302,442 issued Nov. 17, 1942 shows a tubular, reciprocating sliding valve disposed atop a piston head. The valve slides in an axis generally perpendicular to the axis of the lower drive piston.
U.S. Pat. No. 5,694,890 issued to Yazdi on Dec. 9, 1997 and entitled “Internal Combustion Engine With Sliding Valves” discloses an internal combustion engine aspirated by slidable valves. Tapered, horizontally disposed valve seats are defined near inlet and exhaust ports at the top of the combustion chambers. The slidable valves are tapered to conform to the valve seats. Valve movement is caused by a crankshaft driving a rocker arm that is oriented substantially orthogonal to the rod, whereby crankshaft rotation is translated into horizontal, sliding movements of the planar valves, which reciprocate in a direction normal or transverse to the axis of the piston.
U.S. Pat. No. 7,263,963 issued to Price on Sep. 4, 2007 and entitled “Valve Apparatus For An Internal Combustion Engine” discloses a cylinder head with a cam-driven valve slidably disposed within a valve pocket. The valve, which is displaceable along its longitudinal axis has a tapered portion defining multiple fluid flow passageways. The valve is displaced by cam rotation between a configurations passing gases through the passageways and a configuration wherein the valve flow passageways are closed.